This invention relates to a circuit for controlling a meter movement having a pointer movable over a variable value indicating scale divided into different segments having different degrees of compression or expansion.
Most voltmeters or ammeters have separate indicating scales for different ranges of variable values to maximize the accuracy of the meter indications. A range switching control is provided for changing the sensitivity of the meter movement in the various ranges of operation thereof. It has heretofore been recognized that it is often convenient to provide only a single scale for a wide range of voltage or current values, and to obtain reasonable accuracy in measurement over the entire scale by dividing the single scale into different segments having different degrees of compression or expansion, thereby avoiding the necessity for range switching. For example, a scale for indicating a current range of from 0 to 5 milliamps can be divided into four segments, the first segment indicating the range of from 0 to 5 microamps, and the successive segments indicating the ranges of from 5 to 100, 100 to 1,000, and 1,000 to 5,000 microamps, respectively. However, the design of a relatively inexpensive reasonably accurate meter control circuit which can be readily adjusted for calibrating the meter within each scale segment poses difficult problems which have not been completely satisfactorily solved by the prior art. Examples of such prior art meter control circuits for controlling the movement of a pointer over a scale divided into segments having different compression ratios are disclosed in U.S. Pat. Nos. 2,824,286 and 4,011,504. In these circuits, the calibration procedures are cumbersome primarily because the adjustments made for calibration over one scale segment affect the indications produced on other scale segments.